1. Title: Effects of Sodium Bicarbonate Ringer's Injection and Sodium Lactated Ringer's Injection on postoperative acute kidney injury in patients undergoing major abdominal surgery: a randomized, controlled, open-label clinical study 2. Objective: To evaluate the effect of BRS and LRS infusion on acute renal injury in patients undergoing major abdominal surgery 3. Primary outcome: Incidence of AKI at 28 days postoperative (defined as acute kidney injury, according to Kidgo 2012 definition and classification). 4. Study Design: Randomized, controlled, open-label clinical study.